Many physical and biochemical factors combine to control the process of inflammatory leukocyte recruitment in the microcirculation. While the roles of molecular mediators and hemodynamics on leukocyte adhesion and extravasation are more or less understood individually, the complex, nonlinear interaction between these factors is less so. This project focuses on integrating multiple factors affecting rates of leukocyte recruitment such as microscale hemodynamics, leukocyte deformation, and spatial distributions of adhesion receptors, into biomimetic experiments and state-of-the-art computer simulations of cell adhesion under flow. In Aim 1 we will conduct flow adhesion experiments with human neutrophils flowing through microfabricated branching conduits with circular cross-section and selectin-coated surfaces, to understand the physics of leukocyte margination and rolling throughout the microvascular network. These results will be compared to theoretical predictions of an improved version of multiparticle adhesive dynamics and ultimately to in vivo experiments in mouse models of inflammation. In Aim 2 we will further extend the computer simulation to consider viscoelastically deforming neutrophils and the role of cell flattening in stabilizing selectin and integrin-mediated adhesion to the endothelium. The theoretical model will be validated with micropipette experiments of neutrophil compression under various cytoskeletal modifiers, and then used to help interpret flow chamber adhesion experiments to selectin and integrin-presenting surfaces where the contact area under rolling neutrophils is measured by viewing interactions from the side. These studies will address our hypothesis that cell flattening acts to stabilize rolling adhesion and that downregulation of either neutrophil or substrate adhesion receptors can disrupt this stabilization. Finally, in Aim 3 we will use microcontact printing methods to systematically study how relative spatial distributions of selectin and integrin ligand molecules on model endothelium act to control the dynamics of leukocyte adhesion and the ultimate location of leukocyte firm arrest. The proposed work of this project will use engineering methods to integrate current knowledge of leukocyte-endothelial interactions into a more complete picture of inflammation in vivo.